The present invention relates to an arrangement for controlling the steering angle of a motor vehicle, and more particularly, to a steering angle control arrangement having a user-controllable operating element, a vehicle longitudinal speed sensor system, and a steering angle adjusting device which is coupled such with the vehicle longitudinal speed sensor system and the operating element that the desired steering angle value is determined as a function of the control force exercised on the operating element and of the sensed vehicle longitudinal speed.
In known steering angle control arrangements as used, for example, in automobiles, the desired steering angle value for the steering angle adjusting device is variable as a function of the control force exercised on the operating element as well as of the momentary longitudinal vehicle speed. Such an arrangement replaces, for example, a conventional steering system having a steering wheel and a steering angle adjusting device mechanically connected thereto in the case of automobiles, as a result of which comparatively short adjusting paths and high adjusting speeds can be achieved.
Operating elements, as they are used here and on which the control force is exerted to influence the determination of the desired steering angle value, are called isometric operating elements. According to whether the operating element is arranged in a rigid manner or, for providing an intuitive acknowledgment of one or several quantities representative of driving dynamics, is arranged to be deflectable, it is called a passive or active operating element. For fulfilling a satisfactory steering functionality, these operating-element-related characteristics are preferably combined with a speed-dependent steering ratio; i.e., the desired steering angle value is, in addition, determined as a function of the respective actual longitudinal vehicle speed.
In these steering angle control arrangements, no direct mechanical connection exists between the operating element and the steering angle adjusting device and thus the controlled vehicle wheels. Consequently, the driver loses the acknowledgment with respect to the respective steering condition which is normally transmitted by way of this connection. Various attempts have been made to compensate for this loss. In, for example, U. Bolte, "The Active Adjusting Part--an Ergonomic Operating Concept", Fortschr.,-Ber. VDI Series 17, No. 75, Dusseldorf, VDI-Verlag 1991, the deflection of the operating element as a function of the yaw velocity is, for example, suggested as the acknowledgment. Because this yaw velocity is a linear function of the longitudinal speed of the vehicle, however, the operating element deflection used as the driver information changes during braking or accelerating already in a curve with a constant radius to which the driver is not accustomed. In the steering angle control described in DE 196 00 139 C1, which is not prior art, a reaction force is exercised which counteracts the control force and which increases with a rising amount of the steering angle as well as with an increasing longitudinal vehicle speed.
U.S. Pat. No. 3,022,850 discloses an arrangement which uses a control stick, among other things, for adjusting the steering angle. For this purpose, the pertaining control stick deflection signal can be amplified as a function of the speed, specifically preferably inversely proportionally to the square of the longitudinal speed so that, independently of the longitudinal vehicle speed, a certain control stick deflection results in an essentially constant lateral acceleration.
DE 44 03 379 A1 discloses a steering system in which the ratio between the rotation angle of a steering wheel and the thus adjusted steering angle of steerable vehicle wheels can be changed as a function of the longitudinal vehicle speed to achieve, in a low to medium speed range, a sensitive steering reaction and, in a high speed range, a good stability of the steering. For this purpose, the transmission ratio of a pertaining steering gear is acted upon in a suitable manner.
In DE 196 25 498 C1, which is not prior art, an example of a steering control device is also described in which the desired steering angle value is given only as a function of the control force exercised on the operating element. Operating element deflection devices are provided which deflect the operating element corresponding to the respective existing actually steering angle value.
An object of the present invention is to provide an improved steering angle control arrangement which results in high operating comfort and high operating reliability.
The foregoing object has been achieved in accordance with the present invention by providing a steering angle control arrangement having control element deflection devices which deflect the operating element corresponding to the respective existing actual steering angle value. In this arrangement, the desired steering angle value is, on one hand, given as a variable function of the control force exercised on the operating element as well as as a function of the momentary longitudinal speed of the vehicle and, on the other hand, the operating element is deflected by suitable operating element deflection devices corresponding to the respective existing actual steering angle value and therefore independently of the vehicle longitudinal speed.
Consequently, the present invention results in the longitudinal-speed-dependent desired steering angle value indication being caused without any effect on the acknowledgment of the steering condition to the operating element. Thereby, under certain conditions, such as constant slip angles and a neutral steering tendency of the vehicle, this reaction advantageously does not change when driving a curve with a constant radius even if the longitudinal speed of the vehicle changes during this driving.
According to another aspect of the present invention, the actual steering angle value is detected by a suitable path sensor system by way of the movement of a tie rod which, as part of the steering angle adjusting device, is coupled to the steerable vehicle wheels. The desired steering angle value is indicated by a corresponding generator which, for this purpose, receives the information concerning the operating element control force from a pertaining sensor and by way of the momentary longitudinal speed of the vehicle from the corresponding vehicle longitudinal speed sensor system.
In yet a further aspect of the arrangement according to the present invention, the tie rod path sensor system is formed by a hydraulic path measuring cylinder, and the operating element deflection devices include a hydraulic cylinder configured as an actuator which is hydraulically coupled with the path measuring cylinder.